1. Field of the Invention
The present invention relates to hubs for torsion damping devices comprising a predamper, especially for motor vehicles
It also relates to torsion damping devices equipped with the said hub, described for example in the document FR-A-2 693 778 (U.S. Pat. No. 5,601,173) to which reference may be made for further details.
2. Description of the Related Art
As is known (FIGS. 1 to 3), such a hub 3 constitutes the output element of the torsion damping device. The hub 3 is surrounded by two guide rings 1, 2 which are disposed on either side of a damper plate 4, which also surrounds the hub 3 but with circumferential loose coupling means 60 interposed, the latter comprising a denture, that is to say alternate teeth and recesses, which are conventionally of trapezoidal form and which are formed at the outer periphery of the hub 3, together with a denture consisting of alternate teeth and recesses, which are conventionally of trapezoidal form and are formed at the inner periphery of the damper plate 4. The teeth of the damper plate 4 penetrate, with a clearance, into the recesses of the hub 3 and vice versa. The hub 3 is splined internally for coupling it in rotation with a first shaft.
The guide rings 1, 2 are joined together through spacers 8 which extend with a circumferential clearance through notches 7 formed at the outer periphery of the damper plate 4. The spacers 8 may take another form, and may consist of axial lugs projecting from one of the guide rings and fixed to the other guide ring, for example by seaming.
The guide rings 1, 2 are fixed to the input element 16 of the said damping device. This input element 16 is fixed for example to a reaction plate which is mounted on a second shaft, for rotation with the latter, either directly or, in this example indirectly through friction liners 31, 32 which are divided into pads 41, 42 fixed by rivets 47 on blades 17 which extend outwardly the input element 16 which is in the form of a disc. The liners 31, 32 may of course be of endless form. In the case of an application to a motor vehicle, the first shaft is typically the input shaft of the gearbox and the second shaft the crankshaft of the engine, the liners 31, 32 being arranged to be gripped releasably between the pressure and reaction plates of a clutch. For this reason the hub must be able to slide axially along the first shaft.
The torsion damping device in this example comprises an input element 16 which is coupled elastically to the output element 3 (i.e. the hub) through a main damper including guide rings 1, 2 and the damper plate 4, together with a predamper which includes the damper plate 4 and the hub 3 (i.e. the output element).
Circumferentially acting resilient means 5, 9, which in this example consist of coil springs, together with axially acting friction means 20, are interposed operatively between the guide rings 1, 2 and the hub 3.
The springs 5 are mounted in windows (not given a reference numeral in FIG. 1) which are formed in facing relationship with each other in the rings 1, 2 and the damper plate 4.
These springs 5 are part of the main damper and are stiffer than the springs 9 which are part of the predamper. These springs 9 are mounted in open slots 91, 92 formed in facing relationship, respectively, at the inner periphery of the damper plate 4 and at the outer periphery of the hub 3.
The slots, which are of generally swallowtail form, and the springs 9 bear on the circumferential edges of the slots through interposed inserts 90, the dorsal face of which is of dihedral form in order to cooperate with the said edges, defining a point when the damper plate 4 and the hub 3 are in the rest state. The front faces of the inserts 90, which are preferably of plastics material in order to reduce noise, carry retaining and centring spigots each of which is engaged in a spring 9 of the predamper.
The friction means 20 comprise a resilient ring 56, which in this example is a corrugated ring, which bears on the guide ring 2 and on an application ring 55 in contact with the damper plate 4, so as to grip a friction ring 57 by reaction between the damper plate 4 and the disc 16 which is backed on the damper plate 1. The rings 55 to 57 are part of the main damper and act during relative rotating movement between the damper plate 4 and the guide rings 1, 2. This movement is only produced when the damper plate 4 comes into engagement with the hub 3 after the circumferential clearance of the loose coupling means 60 has been taken up, because the springs 5 are stiffer than the springs 9 of the predamper. Shocks therefore occur as the clearance in the loose coupling means 60 is being taken up.
The application ring 55 and the friction ring 57 are coupled in rotation respectively to the guide ring 2 and the guide ring 1. For this purpose, each of the rings 1, 2, which in this example are identical, has holes 54 through which there pass lugs 58 and spigots 59 which project respectively from the application ring 55 and the friction ring 57, so as to obtain the said coupling in rotation. Each spigot 59 does of course extend through an aperture in the disc 16.
A centring bearing 51 is interposed between the outer periphery of the hub 3 and the inner periphery of the guide ring 1. A resilient ring 61, which in this example is a Belleville ring, a friction ring 52 and a metallic insert ring 53 are interposed between the outer periphery of the hub 3 and the inner periphery of the guide ring 2.
The bearing 51 and the ring 52 have an L-shaped cross section and include thickened portions, each of which is engaged in the known way in a notch formed in the inner periphery of the guide ring 1, 2 concerned, so as to couple the bearing 51 and the ring 52 respectively in rotation with the guide ring 1 and the guide ring 2.
The components 51 to 53 and 61 are located radially inwardly of the rings 55 to 57 of the main damper. These components 51 to 53 and 61 act permanently during relative motion between the input element 16 and the output element 3. The spring 61 has a lower stiffness than the spring 56. The spring 61 has a stiffness such that it does not overcome the action of the low stiffness springs 9.
The notches housing the springs 9 interrupt the dentures of the loose coupling means 60 with their circumferential clearance. The hub 3 has at its outer periphery a shouldered flange in which the denture of the hub 3 is formed.
The torsion damping device operates in the following way during relative movement between the input element 16 and the output element 3:
in a first step, since the springs 5 are stiffer than the springs 9, the predamper operates by itself so as to absorb the vibrations in the slow running mode of the engine, so that the springs 9 are compressed with relative movement firstly of the damper plate 4 with respect to the hub 3, and secondly of the bearing 51 and the ring 52 with respect to the hub 3; this movement is continued until the teeth of the damper plate 4 come into engagement with the teeth of the hub 3;
in a second step, the damper plate 4 is coupled to the hub 3 for rotation together because the clearance in the loose coupling means 60 has been taken up, and relative movement occurs between the guide rings 1, 2, the damper plate 4 against the action exerted by the springs 5 and the rings 55 to 57; this movement is continued until the spacers 8 come into abutment against the edges of the slots 7, or until interlocking occurs between the turns of the stepped action springs 5 which in this example are disposed in pairs in the windows of the damper plate 4 and guide rings 1, 2.
When the friction liners 31, 32 are released, the hub 3 slides axially along the splines of the driven shaft by virtue of its rotary coupling splines.
Thus the hub 3 must be sufficiently strong at its outer periphery to be able to cooperate with the damper plate 4, which is a hardened component for housing the springs 5. At its inner periphery the hub 3 must have good sliding properties. These two requirements lead to a compromise as regards the choice of material for the hub 3. This is even more so to the extent that the hub 3 undergoes shocks when the teeth of the damper plate 4 come into engagement with the teeth of the hub 3.
The choice of the material therefore depends on the resulting work hardening effects.
In addition, for a given external denture the hub may have different forms, which does not enable manufacture to take place in long production runs.
In this connection, the thickness of the hub is a function of the application, and in particular of the outer diameter of the shaft with which the hub cooperates. The axial position of the flange of the hub depends also on the application.
An object of the present invention is to standardise the hub as far as possible in a simple and inexpensive way, without any limitation as to the choice of material for the hub.
According to the invention, a hub of the type described above is characterised in that it comprises two distinct and concentric coaxial parts, namely an external flange having the denture of the loose coupling means and an internal sleeve having the internal rotary coupling splines, in that the flange has a tubular form at its inner periphery, being shorter in the axial direction than the internal sleeve, and in that the inner periphery of the external flange is fitted around the outer periphery of the internal sleeve, with axial stop means being interposed for preventing any axial sliding movement of the external flange with respect to the internal sleeve.
According to the invention, a torsion damping device is characterised in that it is equipped with such a hub.
Thanks to the invention, the flange or outer body and the internal sleeve may be of different hardnesses matched to their function.
Thus the sleeve can be of a material having good sliding properties, while the outer flange can be of a material having the desired hardness.
Since the sleeve is longer in the axial direction than the flange, it is possible to position the flange axially with respect to the sleeve according to the application, that is to say to regulate its axial offset.
The external flange is thus a standardxe2x80x94identicalxe2x80x94component according to the type of predamper, while the internal sleeve is an adaptor and support member the thickness of which varies according to the application as do its splines. In this case the length of the sleeve is constant, that is to say it is standard.
The invention enables production runs of the flange to be extended.
It will be appreciated that the sleeve is a simple and inexpensive component. Due to its standardisation the flange is also less expensive. It also enables the denture of the damper plate of the torsion damping device to be standardised. The form of the flange does of course depend on the type of predamper used.
The flange and the sleeve can be made from sintered material, which thus enables all sharp edges to be avoided. The flange may be force-fitted on the sleeve, or adhesively bonded or welded on the latter. In another version it may be formed by superimposed moulding.
The following description illustrates the invention with reference to the attached drawings, in which: